An optical trap is an optical tool that utilizes the gradient forces of a focused beam of light to manipulate particles with dielectric constants higher than a surrounding media. To minimize energy, the particles move to where an electric field is the strongest.
Optical trapping is used to manipulate particles, such as cells and nucleic acids. Trapped particles are typically suspended in a fluid medium. The fluid can create unwanted optical aberrations in the optical path and degrade performance.
There are a number of different approaches used for creating optical traps. In one approach, a single laser beam is focused to create one optical trap. The beam remains stationary and a device used to hold the particles, such as a microscope slide, is mechanically moved. In this technique, the optical system is static and any movement is made through mechanical means such as a precise motorized stage. Only a single trap can be created with this approach.
In another approach, a single laser beam is focused to create one optical trap and the trap is moved in two dimensions by means of a scanning mirror. For example, the mirror can be moved at a high speed by two actuators under computer control. A single particle can be trapped and then moved by the scanning system. Furthermore, multiple particles (typically up to 8 effectively) can be trapped by rapidly scanning the laser beam between the trapped particles. Essentially, rapidly moving the beam using the scanning mirror results in “time sharing” of one laser beam over multiple particles. Only a single trap can be created with this approach.
In yet another approach, multiple laser beams are created using a spatial light modulator (SLM). The multiple beams can then be controlled by the SLM. The SLM is composed of cells, each of which can be addressed electronically from the computer. The computer can then control the refractive index of each cell which in turn controls properties of each beam. Using this approach, multiple particles can be trapped and individually controlled. However, this method is indirect and typically requires a complex and relatively slow algorithm to compute trap positions.
Grier et al (U.S. Publication No. 2005/0001063) disclose a method and apparatus for laterally deflecting and separating a flow of particles using a static array of optical tweezers. While the beam can be controlled, control is not done in real-time.
It is an object of the present technology to address deficiencies in the prior art and to provide other advantages.